1. Field of the Invention
The present invention relates to radiation therapy. More particularly, the present invention relates to the calibration and quality assurance of radiation delivery.
2. Background of the Invention
Cancer is a group of diseases in which abnormal cells divide without control, often invading other tissues. According to the American Cancer Society, in 2007 in the United States alone there will have been an estimated 1,444,920 new cases of cancer. It is estimated that in that same period 559,650 people will die in the United States due to various forms of cancer. Many forms of treatment are available and continue to be discovered. One of these forms of treatment is radiation therapy which is used, often in combination with other types of treatment, on roughly half of all cancer sufferers.
Radiation is often utilized in the treatment of cancer in order to control malignant cells and shrink tumors. Due to its harmful effects, physicians often attempt to limit the radiation to other parts of the body. This is accomplished by focusing the radiation on the tumor itself. However, the radiation field often may include normal tissue around the tumor to allow for uncertainties in the position of the tumor. One cause of these uncertainties is the natural movement of organs in the body which cause the position and shape of the tumor to change. Unfortunately, by increasing the field of the radiation, the normal tissue can also be affected. Radiation to these areas may cause side effects during treatment, in a period of time after the treatment, or cumulative side effects from re-treatment. To avoid this result, shaped radiation beams are often aimed from several angles to intersect at the tumor. Because these beams do not change direction with the movement of the tumor, excess radiation is received in a marginal volume around and including the tumor and its possible spatial deformation and positions.
Newer techniques allow for radiation to be aimed such that it follows the movement of the tumor and synchronizes the delivery of the radiation with this movement to limit the excess radiation. The equipment for this process is very complex and even small deviations can have large repercussions. To avoid these deviations, the equipment must frequently be calibrated and the quality of the results must be assured.
In radiation protection, or health physics, a phantom is a device that simulates the human body or part of the human body and is used to calibrate or test the calibration of a detector that measures radiation emanating from within the body. Phantoms can be used in the calibration of radiation delivery devices. However, most phantoms do not provide an accurate representation of the movements internal to the human body and the movement of a tumor within the body. Thus, the calibrations of these radiation delivery devices are not as accurate as they might be particularly with regard to the calibration of systems and methods employed and embodied in these devices to track patient, organ, and tumor/target motions.
In a living human patient, such motions may not always be predictable, having apparently spontaneous variation in rate, depth, etc., due to complex physiological, somatic, and psychological controls. A phantom that can simulate organ and tumor/target movement within the moving body in a more lifelike manner allows the proper calibration and quality assurance of such radiation delivery devices that track organ, tumor/target, and body motion and consequently and programmatically adjust radiation delivery. Furthermore, the organ, tumor/target, and body motion should include both predictable and spontaneous movements to accurately mimic the s of same of an actual human patient.